Question

If the radius of a circle is doubled area is multiplied by

Answer 1

Let radius be r
Therefore
$area \: of \: circle = \pi \times r {}^{2}$
Now radius is doubled
So
$area \: of \: circle = \pi \times ( 2r) {}^{2} = \pi4r {}^{2}$
So area becomes 4 times .

Answer 2

Let the radius be r.

Area=$\pi r^{2}$

Since radius is doubled.

Now the increased area is=$\pi (2r)^{2}$

The area becomes =$\pi 4r^{2}$

So the number to be multiplied=$\frac{\pi r^{2}}{\pi 4r^{2}}$

=4

Thats the answer.